Photovoltaic and Thermal Energy System With Improved Tracking

ABSTRACT

An improved diurnal sun tracking system and methodology for use with a photovoltaic solar collector system mountable on flat roof industrial buildings or multi-unit apartment buildings is provided. The improved tracking system and method rotates or pivots the solar collector system to track the sun during the spring and fall Equinoxes in a first tracking mode, as well as from winter to summer solstices, when the angular rate of the sun&#39;s movement does not exactly follow the angular rate at the Equinoxes, in a second tracking mode.

FIELD OF THE INVENTION

The present invention relates to photovoltaic and thermal energy systems, and more particularly to an improved system for diurnal sun tracking usable in combination therewith.

BACKGROUND

The overall efficiency of a photovoltaic system is the product of the system's reflectance efficiency, thermodynamic efficiency, charge carrier separation efficiency and conductive efficiency. However, conventional photovoltaic systems generally employ fixed flat plate solar panels mounted at the latitude angle. These systems are inefficient with regard to a cost per watt for photovoltaic systems. Since there is an ever-increasing need to produce more energy at a lower cost, there is correspondingly a need in the art for an improved photovoltaic system which exhibits an improved overall efficiency, as compared to convention flat plate panel systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cylindrical pyramid optic concentrator made up of faceted flat sections to spread the sun's irradiance evenly on the solar cells, with solar cells and domestic hot water or space heating, in accordance with the principles of the invention;

FIG. 2 illustrates two examples of diurnal tracking systems recessed into a south facing pitched roof, schematically illustrating a diurnal tracking recessed system using either a faceted cylindrical optic, or ½ Fresnel lens showing a diurnal clock drive, a connecting strut, and a copper tube for water or space heating;

FIG. 3 illustrates a 34 solar cell string, arranged in a line and connected in series;

FIG. 4 illustrates sun trajectories at 32 degrees south latitude from a reference;

FIG. 5 illustrates sun elevation angular trajectory within concentrator field at 40 degree north latitude (derived from the FIG. 4 reference);

FIG. 6 illustrates an extruded acrylic linear Fresnel lens in combination with piano reflective surfaces;

FIG. 7 illustrates a cylindrical faceted concentrator configuration with a 17 cell string;

FIG. 8 illustrates a flat roof mounting of a Fresnel lens concentrator system;

FIG. 8A illustrates the diurnal tracking configuration of the system illustrated by FIG. 8;

FIG. 9 depicts a simplified diagram for an improved sun tracking circuit, configured in accordance with the principles of the invention; and

FIG. 10 depicts a rear view of a solar cell string, configured in accordance with one or more embodiments of the invention.

BRIEF SUMMARY OF THE INVENTION

Disclosed and claimed herein are systems and methods for improved sun tracking for use with roof-mounted solar collector modules. In one embodiment, a system includes at least one roof-mounted solar collector module and an attached stepper motor that is configured to pivot the solar collector module along a direction of movement of the sun. A digital driver circuit electrically coupled to the stepper motor is configured to actuate the stepper motor. Additionally, the system includes a sensor to detect sun irradiance and, in response, provide an alignment signal corresponding to a current alignment of the solar collector module in relation to a position of the sun. The system further includes a sun tracking circuit electrically that is configured to receive the alignment signal from the sensor, and actuate the digital driver circuit according to a first mode when the alignment signal indicates that the current alignment of the solar collector module matches the position of the sun. Additionally, the sun tracking circuit is configured to actuate the digital driver circuit according to a second mode when the alignment signal indicates that the current alignment of the solar collector module does not match the position of the sun, where at least one of a speed and a direction of pivoting of the solar collector module is different in the second mode than in the first mode.

Other aspects, features, and techniques of the invention will be apparent to one skilled in the relevant art in view of the following detailed description of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

A combined diurnal tracking, concentrator, photovoltaic electrical generation system/domestic hot water or space heating solar thermal system is mountable on flat roof industrial buildings; flat roof multi-unit apartment buildings, and pitched roofs of single family residences. The systems, configured in accordance with the principles of the invention, may be exclusively diurnal in which the sun is tracked on a daily basis.

One aspect of the invention is to achieve a substantial reduction in the cost-per-watt for photovoltaic systems as compared to flat plate panels by reducing the number of solar cells required for a given power output by almost 3/1 or 6/1. The increased heat generated by a 3/1 or 6/1 concentration of the sun's insolation on the solar cells may be drawn off by an anti-freeze fluid circulated in an aluminum extrusion, to which the solar cells and the pyramidal concentrator reflectors are attached. This coolant is used to provide domestic hot water heating, thus providing additional cost savings for the user as well as making the solar cells more efficient, by keeping them cool.

Another aspect of the invention is to move the solar array in elevation to coarsely track the sun from winter to summer solstices in the seasonal tracking mode, or pivoted from sunrise to sunset in the diurnal tracking mode using an improved tracking circuit and methodology for tracking the position of the sun. This provides the additional advantage of achieving ideal near normal incidence of sunlight in one axis on the system throughout the year, as compared to fixed flat plate solar panels mounted at the latitude angle. For the diurnal tracking configuration, there is an improvement in energy collected throughout the day by an approximate factor of 1.27 relative to fixed angle flat plate collectors. The combined electrical energy generation improvement of the solar tracking and the heat removal at the summer solstice may approximately 40%.

Still another aspect of the invention is a faceted cylindrical pyramid optic concentrator which comprises a combined photovoltaic/domestic hot water or space heating concentrator-collector unit, as shown in FIG. 1. The insolation incident on the pyramidal concentrator is reflected to commercially available, >17% efficiency solar cells currently available, with a concentration ratio of 3/1. In certain embodiments, four cell arrays using standard flat plate panel processes have been fabricated using these cells by SPIRE Inc. In production, 17-cell or 34-cell series strings similar to those currently in production for flat plate panels have been fabricated and will be used.

In order to generate 0.68 Kwatt at local noon, six 17-cell modules using the faceted cylindrical concentrator optics are required. As is shown in FIGS. 1 and 8, these can be arranged in rows, in the north-south direction, on flat roofs or ground installations for industrial applications, thus minimizing wind loads relative to conventional flat plate collectors without domestic water heating. As can be seen in FIG. 1, for hot water applications, the 17-cell arrays are mounted to aluminum extrusions into which copper tubes are snapped. These aluminum extrusions/copper tubing provide additional rigidity for large panels and are used as the frame for mounting multiple modules on roofs through a single axis elevation tracking system. Either anti-freeze (or potable water in non-freezing areas) may be flowed through the copper tubes, resulting in the waste heat generated by the solar cells with the concentrated insolation being drawn off to heat domestic hot water or provide domestic space heating. It is estimated that a 220-watt electrical system will provide enough waste heat to heat water in an 80 gallon tank from 54° F. to 120° F. in one sunny day. This provides a dual function of providing domestic hot water at close to 70% conversion efficiency (achieved by the 6/1 concentrators with mostly optical reflection/transmission losses), while at the same time generating direct current electricity for use in grid-tied photovoltaic solar systems currently used in residences, or battery-backup co-generation facilities for minimizing peak power usage in industrial applications. In addition to its economic advantages, the removal of heat from the solar cells for hot water heating also advantageously reduces the operating temperature of the solar cells, thereby improving their efficiency. Typical efficiency losses of silicon cells are 0.5% per ° C. above 26° C. Therefore, in the summer, by cooling the cells to 25° C., such as in heating a swimming pool, this system will provide a 12.5% improved output as compared to conventional uncooled flat plate panels, which can heat up to 50° C. A depiction of an early prototype of a 17-cell faceted cylindrical concentrator version of the system disclosed herein is shown in FIG. 7.

FIGS. 8 and 8A illustrates how the diurnal tracking configuration may be mounted on a flat roof. As can be seen, there are no roof penetrations for mounting the solar array, thus eliminating possible leaks caused by the mounting of the solar array. The array may be secured to the roof in the presence of wind using “sleepers” made up of wood or galvanized steel angles. The arrays may be secured to the roof by the greater than 200-pound combined weight of the optical arrays and the counterweight for each pivoted module. Larger north-south dimensions of the roof repetitions of the basic array shown can proportionally increase its power output. Also, by repeating the array in the east or west direction, the power output can also be increased proportionally.

FIG. 2 shows the recessed mounting of the diurnal tracking configuration between the roof rafters on a south facing pitched roof with a slope of the local latitude±5° for optimum performance, while also improving its aesthetics. In addition, the orientation of the pitched roof to due south can vary by as much as ±15°, without significant losses in diurnal energy generation.

In certain embodiments, the diurnal tracking mechanism may be comprised of a 1600 step/revolution stepper motor driving a digital driver that operates in one of at least two modes—a first mode and a second mode—the details of which are described below with reference to FIG. 9.

A diurnal tracking configuration, designed for flat roofs, is shown in FIG. 8. In this configuration, the reflective side panels are piano mirrors and a cylindrical Fresnel lens extruded from acrylic material, focuses the sun in a blurred line image caused by chromatic aberrations behind the 34-cell array. As also shown in FIG. 6, the Fresnel lens has dimensions of 30″×108″. This 108″ lens dimension allows the sun to move from winter to summer solstice for the recessed pitched roof configuration shown in FIG. 2, while still passing through the Fresnel lens concentrator and reaching the 86 inch long, 34-cell array under full concentration. Any rays that would miss the array in the East-West direction, due to slight variation in the tracking accuracy and/or lens chromatic aberrations, are still directed to the 34-cell array by the piano side mirrors. The concentration ratio of the Fresnel lens is 30/5=6/1, results in a further reduction of the number of solar cells per output watt by an additional factor of 2/1, as compared to the 3/1 faceted cylindrical concentrator configuration, thereby further reducing the relative cost of this system component, and allowing more efficient cells at a higher cost/cell to be used.

As discussed herein, the preferred optical arrangement for the diurnal tracking system of the present invention employs a Fresnel lens, which is a combination of two extruded acrylic half lenses cemented together, and piano reflective mirrors, for focusing incoming rays of sunlight onto the solar cells for reducing the number of solar cells necessary to produce a desired power output. This configuration is necessary to reduce the cost of the Fresnel lens extrusion die, the cost of which increases exponentially with the width of the extrusion. FIG. 8A illustrates the Fresnel lens piano reflective surface optical arrangement; and FIG. 8A also illustrates diurnal tracking in which the optical concentrator is pivoted by the stepper motor clock drive discussed earlier, between a first position in which incoming rays of sunlight are incident to the front surface thereof at sunrise (e.g., 7:20 AM) to a second position in which incoming rays of sunlight are incident to the front surface at sunset (e.g., 4:40 PM), the concentrator being pivoted throughout the course of the daytime hours to track the position of the sun. The speed and timing of such pivoting may preferably proceed in accordance with the improved diurnal sun tracking methodology disclosed herein, and more particularly described below with reference to FIG. 9.

FIG. 8A also illustrates tubing coupled to the photovoltaic system for the flow of fluid to remove heat from the solar cells, and to also provide hot water or space heating. FIG. 6 illustrates the Fresnel lens employed as the concentrator for the photovoltaic system, illustrating Fresnel facets extruded on the inside surface of the lens. FIG. 8 also illustrates the aluminum extrusion on which the solar cells are mounted, and into which the tubing for the fluid coolant is connected. As is shown in FIG. 8, preferably, the optical elements are mounted on a flat roof in a “checkerboard” pattern to minimize shading near noon.

FIG. 2 illustrates a configuration of this system for diurnal tracking for south facing pitched roofs. The pivot axis for these collectors are mounted near the window to capture sun for a maximum time period of 7:30 A.M. to 4:30 P.M. with full output and partial output outside this hourly range. The advantage of this approach for the faceted cylindrical reflective configuration is that separate windows on the collectors are not needed.

In accordance with the principles of the invention, one or more of the following advantages may be realized:

-   -   1. The system may use highly efficiency silicon solar cells         currently in production, thus requiring a smaller number of         cells for a given power output, thereby reducing solar panel         area.     -   2. The concentrator may reduce the number of cells required for         a given wattage by a factor of over 2.5/1, or 5/1, thus reducing         the highest cost item in a photovoltaic solar panel by at least         these ratios.     -   3. By mounting the encapsulated cells directly to the aluminum         extrusion using thermally conducting paste or thermal conducting         interface sheets, and not permanently bonding them to the cover         glass as is prevalent in flat plate collectors, solar systems         can be economically upgraded with more efficient solar cells as         they become available, an advantage which is impossible with         flat plate solar panels.     -   4. The high elevation angle of the plane of the window or         Fresnel lens at the beginning and/or end of the diurnal tracking         day may allow any snow buildup to slide off, thereby eliminating         the zero energy collection applicable to snow covered fixed flat         plate solar panels.     -   5. The waste heat generated by the solar cells may be collected         by a solar thermal aluminum substrate containing copper tubes,         which provides domestic hot water heating at close to 70%         efficiency, while removing excess heat from the solar cells to         increase the efficiency of operation thereof, thus providing         additional economic justification and reducing the overall         payback period.     -   6. The hot water or space heating extrusions “pay their way” by         providing housing rigidity normally provided by the extra cost         aluminum housings of flat plate panels.

Experimentation has identified a potential limitation in obtaining the required current output from conventional solar cells as a result of limitations in the conductivity of the ribbon wire used to route the current generated in the cells out to the collector terminals. Modifications to the construction of standard cells used for non-concentrating cells in flat plate collectors can mitigate the limitations. More specifically, use of thicker and wider ribbons and more “fingers” in the solar cell will reduce the combined cell and ribbon resistance by a factor of approximately 10/1. A preferred method of solving this high current problem is to use standard 125 mm×125 mm solar cells cut in half to 62.5 mm×125 mm, arranged in strings as shown in FIG. 1, or in thirds, as shown in FIG. 10. These arrangements respectively double or triple the voltage per each string, and correspondingly halve or third the current, while maintaining the same power output, thereby easing the requirements for reducing the resistance of the conducting ribbons. There are additional considerations in making the ribbon wider since for wider ribbon, some sunlight is prevented from reaching the cell, thereby reducing the quantity of electrical energy generated by the solar cell. Accordingly, a tradeoff is necessary in which optimum combination of ribbon with number of ribbons per cell, ribbon thickness, and “finger spacing” maximize the output power of the cell string. This tradeoff is eased by using www.1366tech.com “corrugated” reflective ribbon, manufactured by Ulbrich, Inc., which directs the reflected solar irradiance back onto the solar cell, thereby compensating for the shadow effect and allowing the use of a wider ribbon to reduce electrical resistance and increase electrical conductivity.

Performance and Cost/Watt

The expected solar power collected by each 17-cell module shown in FIG. 8A using 17% efficiency cells is calculated in Table I. One example of the manufacturing cost of the modules is summarized in Table II. Calculations of diurnal tracking as exposed to flat plate collectors are indicated in Table III.

TABLE I SOLAR POWER COLLECTION (6/1 FRESNEL LENS SYSTEM) Total lens aperture applicable to 1.88 m² solar cell string = Total area of the 40 × 125 mm² cells 0.313 m² Light transmittance of the acrylic 0.85 Fresnel Lens = Concentration ratio with lens (1.88/0.313) × 0.85 = 5.09/1 transmittance = Output of 20% sunpower cells 1000 × 0.313 × 0.2 × 0.85 = without concentration = 53.21 watts Total output of the cells = 53.21 × 5.09 = 270.8 watts

Total Output of One 60-Cell Module=0.271 Kilowatts

TABLE II MATERIAL COST PER 60 CELL MODULE USING SUNPOWER SOLAR CELLS PRORATED FOR A 6-MODULE SET: MATERIALS COST 2 Fresnel lens $250 2 side mirrors $54 1 extrusion $15 1 copper tube $10 1 end Plexiglas $15 1 end mirror $5 channels and angles $10 20 triple sunpower cells $230 5 PC boards $275 misc. plumbing fittings $10 silicone $5 15 Schottky diodes $9 ⅙ tracking stepper motor $15 ⅙ tracking controller $10 ⅙ roof mounting $15 TOTAL MATERIAL COST = $928

For flat photovoltaic panels (and solar thermal panels) the solar power absorbed by the panel degrades proportional to the cosine of the angle between the perpendicular to the panel and the angle to the sun. For a diurnal tracking system the solar collector is always perpendicular IN ONE AXIS to the sun line, in the elevation plane, so the cosine multiplier is always 1.0. The integrated energy for fixed flat plate collectors and a diurnal tracking system in watt-hours is given as follows showing that A diurnal tracking system WHOSE PIVOT AXIS IS MOUNTED AT AN ELEVATION ANGLE OF THE LOCAL LATITUDE, provides 27% more Kilowatt-hours per sunny day as compared to fixed panels:

TABLE III FIXED FLAT PLATE COLLECTOR: DIURNAL TRACKING SYSTEM: IRRADIANCE IRRADIANCE ABSORBED ABSORBED TIME (AT EQUINOX) TIME (AT EQUINOX) 12: NOON 1,000 WATTS/m²   12: NOON 1,000 WATTS/m² 1:00, 11:00 966 WATTS/m² 1:00, 11:00 1,000 WATTS/m² 2:00, 10:00 866 WATTS/m² 2:00, 10:00 1,000 WATTS/m² 3:00, 9:00 707 WATTS/m² 3:00, 9:00 1,000 WATTS/m² 4:00, 8:00 500 WATTS/m² 4:00, 8:00 1,000 WATTS/m² TOTAL: 7.1 KILOWATT-HOURS/m² TOTAL: 9.0 KILOWATT-HOURS/m²

Referring now to FIG. 9, depicted is a simplified diagram for an improved sun tracking system, configured in accordance with the principles of the invention. As shown, system 900 includes a geared stepper motor 910 that is electrically coupled to and driven by a digital stepper motor driver 920, e.g., at 1600 steps per revolution. The stepper motor 910 is further mechanically coupled to a solar collection module (not shown in FIG. 9, but as described above), such that the stepper motor 910 is capable of pivoting the module to track the position of the sun.

The digital driver 920 is further coupled to a power source 930, which in certain embodiments may be a direct current power source, e.g., 12-volt battery. The digital driver 920 is further configured to be driven by clock pulses provided by one or more sun tracking controller(s) 940, which is/are similarly powered by the power source 930. As previously mentioned, the system 900 is configured to track the sun in one of at least two modes—a first mode and a second mode. In the first mode, the sun tracking controller(s) 940 are configured to provide the digital driver 920 with clock pulse at a rate of 1.04 seconds per step in the clockwise direction, which ensures that the solar concentrator module closely tracks the sun at each of the spring and fall Equinoxes. In the second mode, on the other hand, the system 900 is configured to correct for misalignment of the solar collection modules with respect to the sun's position.

References herein to ‘clockwise’ and ‘counterclockwise’ are relative to the direction the sun moves and are reflective of the fact that the shadow of a sun dial moves clockwise in the northern hemisphere (opposite of the southern hemisphere). Thus, ‘clockwise’ movement means movement in the same direction the sun, while ‘counterclockwise’ movement refers to movement in the opposite direction thereof.

It should further be appreciated that the system 900 may preferably be configured to operate only during daytime conditions, e.g., 7:00 am to 4:00 pm. Thus, at the end of the day the system 900 may be configured to cause the solar concentrator module to retrace or pivot back to a predetermined “start of day” position. This “start of day” position may then be preferably maintained until the next morning, at which point the system 900 re-initiates the tracking process. This retracement feature may be implemented by configuring the sun tracking controller(s) 940 with an absolute digital clock (not shown). When the absolute digital clock reaches a predetermined time at the end of the day, e.g., 4:00 pm, a signal may be provided to the digital driver 920 to drive the stepper motor 910 in a counterclockwise direction back to the “start of day” position.

Alternatively, limit switches coupled to the solar collector module may be used to implement the above retracement features. In particular, when the solar collection module reaches the “end of day” position, a first limit switch may cause a relay to be energized and the digital driver 920 to be actuated in the counterclockwise direction. A second limit switch may then be configured to detect when the solar collection module has retraced back to the “start of day” position, at which point the second limit switch is actuated and the digital driver 920 is signaled to stop driving the stepper motor 910. Again, the absolute digital clock timer may be used to determine when the tracking process should re-initiate on the following morning.

Irrespective of the particular design for implementing the retracement function, it may be preferable to perform the retracement at a higher speed (e.g., pulse at 0.01 second per step) than is the case under normal operation of the stepper motor 910.

While operation in the first mode is effective for tracking the sun at the spring and fall

Equinoxes, as the summer and winter solstices approached, the angular rate of movement of the sun does not exactly follow the angular rate at the Equinoxes. To correct for this and maintain precise tracking during these seasonal periods, the sun tracking controller(s) 940 may enter the second mode during which higher speed clock pulses, in either the clockwise or the counterclockwise direction, may be provided to the digital driver 920. While the higher speed at which the system 900 is directed to operate during the second mode may of course vary, in certain embodiments the higher speed may be achieved by the sun tracking controller(s) 940 providing pulses at 0.01 second per step. In this fashion, the solar collector module may be made to pivot either forward or backward to account for the slower or faster angular rate of the sun during such non-Equinox periods.

In order to implement the above-described second mode, the sun tracking controller(s) 940 may be coupled to at least two photocells 950, as shown in FIG. 9, which may be separated by a vane 960. When the solar collection module is directly aligned with the position of the sun, represented as alignment state 970, the two photocells will be roughly equally illuminated, and hence provide essentially equal signals to the sun tracking controller(s) 940. As a result, the sun tracking controller(s) 940 will detect that no correction is needed and continue to operate in first mode with the sun tracking controller(s) 940 providing the digital driver 920 with clock pulse at a rate of 1.04 seconds per step.

If, however, the sun is ahead of the current alignment of the solar collection module, more irradiance will be received by the “front” photocell due to the vane 960 disproportionately blocking the “back” photocell from the sun, and misalignment state 980 will be detected. In response, the sun tracking controller(s) 940 will detect that the module must be pivoted at a faster rate, and correspondingly enter the second mode during which a still clockwise, but faster, clock pulse is provided to the digital driver 920. This will continue until alignment state 970 is again detected by the sun tracking controller(s) 940, at which point the system will revert back to the first mode and the 1.04 second per step tracking rate is resumed.

If, on the other hand, the sun is behind the current alignment of the solar collection module, more irradiance will be received by the “back” photocell due to the vane 960 disproportionately blocking the “front” photocell from the sun, and misalignment state 990 will be detected. In response, the sun tracking controller(s) 940 will detect that the module must be pivoted in the counterclockwise direction, and correspondingly will enter the second mode during which a counterclockwise clock pulse is provided to the digital driver 920. While it may be preferable for this counterclockwise signal to be faster than the normal clockwise signal, it is not strictly necessary since the alignment state 970 will be achieved by the combined speed of movement for the sun and the module by virtue of their opposite directions of movement. In any event, this counterclockwise pivoting will continue until alignment state 970 is again detected by the sun tracking controller(s) 940, at which point the system will revert back to the first mode and the 1.04 second per step tracking rate in the clockwise direction is resumed.

While in the embodiment of system 900, photoconductive photocells are used to detect the sun's irradiance, it should equally be appreciated that any other sensor and related circuitry capable of detecting the sun's irradiance may be similarly used, such as photovoltaic photocells associated with appropriate amplifiers.

Another aspect of improved tracking system 900 is the use of a temperature sensor(s) 995. In particular, the one or more temperature sensor(s) may be used to detect a current temperature of the solar collection module, and provide that information to the sun tracking controller(s) 940. Since excessively high temperatures tend to reduce the efficiency of, and even cause damage to solar cells, in response to detecting that the current temperature of the solar collection module exceeds some predetermined threshold, the sun tracking controller(s) 940 may cause the module to intentionally misalign from the sun's position so as to reduce the amount of incidence irradiance. In certain embodiments, the sun tracking controller(s) 940 may enter the second mode during which higher speed clock pulses, in either the clockwise or the counterclockwise direction, are provided to the digital driver 920. Alternatively, the intentional misalignment of the module may be carried out as a separate and independent routine or mode.

While the above improved sun tracking system has been described with reference to the simplified diagram of FIG. 9, it should be appreciated that the functionality and features of system 900 may be implemented using a wide variety of hardware configurations and/or software routines executed by any number of microcontrollers, processor and the like.

Referring now to FIG. 10, depicted is a rear view of one embodiment of a solar cell string 1000 configured in accordance with the principles of the invention. As illustrated, the solar cell string 1000 comprises a plurality of individual cells 1010 ₁-1010 _(n) connected together via copper cladding 1030 and attached to a PC board substrate 1020. Moreover, in the example of the solar cell string 1000 of FIG. 10, the individual solar cells are configured with rear electrodes. An additional aspect of the design of the solar cell string 1000 is the incorporation of Schottky diodes 1040 ₁-1040 ₃, such that a single diode 1040 is used for every four cells 1010 (e.g., four 40 mm×125 mm cells). This unique design functionally improves the performance of the entire string 1000 by minimizing the effects of single-cell shadowing or low cell output.

While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. 

1. A system for improved sun tracking for use with roof-mounted solar collector modules, said system comprising: a roof-mounted solar collector module; a stepper motor, mechanically coupled to the solar collector module, wherein the stepper motor is configured to pivot the solar collector module along a direction of movement of the sun; a digital driver circuit electrically coupled to the stepper motor and configured to actuate the stepper motor; a sensor configured to detect sun irradiance and, in response, provide an alignment signal corresponding to a current alignment of the solar collector module in relation to a position of the sun; and a sun tracking circuit electrically coupled to the digital driver circuit and the sensor, wherein the sun tracking circuit is configured to: receive the alignment signal from the sensor, actuate the digital driver circuit according to a first mode when the alignment signal indicates that the current alignment of the solar collector module matches the position of the sun, and actuate the digital driver circuit according to a second mode when the alignment signal indicates that the current alignment of the solar collector module does not match the position of the sun, wherein at least one of a speed and a direction of pivoting of the solar collector module is different in the second mode than in the first mode.
 2. The system of claim 1, wherein the speed of pivoting of the solar collector module in the second mode is faster than in the first mode.
 3. The system of claim 1, wherein the direction of pivoting of the solar collector module in the second mode is opposite the direction of movement of the sun.
 4. The system of claim 1, wherein the sun tracking circuit actuates the digital driver according to the first mode by providing clock pulses to the digital driver circuit at a rate of 1.04 seconds per step.
 5. The system of claim 1, wherein the sun tracking circuit actuates the digital driver according to the second mode by providing clock pulses to the digital driver circuit at a rate of 0.01 seconds per step.
 6. The system of claim 1, wherein the sun tracking circuit is further configured to detect a predetermined end of day time and, in response thereto, actuate the digital driver circuit to cause the stepper motor to pivot the solar collector module back to a start of day position.
 7. The system of claim 1, wherein the sensor comprises a first photocell and a second photocell, with a vane disposed there between.
 8. The system of claim 7, wherein the alignment signal indicates that the current alignment of the solar collector module matches the position of the sun when the first photocell detects a similar amount of sun irradiance as the second photocell.
 9. The system of claim 7, wherein the alignment signal indicates that the current alignment of the solar collector module does not match the position of the sun when the first photocell detects a substantially different amount of sun irradiance as the second photocell.
 10. The system of claim 1, further comprising a temperature sensor, electrically coupled to the sun tracking circuit, and configured to detect a current temperature of the solar collection module, and wherein the sun tracking circuit is further configured to cause the solar collector module to misalign from the sun when the current temperature exceeds a predetermined threshold temperature.
 11. A method for improved sun tracking for use with roof-mounted solar collector modules, the method comprising the acts of: detecting sun irradiance incident on a solar collector module, wherein the solar collection module is pivotable along a direction of movement of the sun by a stepper motor; generating an alignment signal, based on said detecting, wherein the alignment signal correspond to a current alignment of the solar collector module in relation to a position of the sun; actuating the stepper motor according to a first mode when the alignment signal indicates that the current alignment of the solar collector module matches the position of the sun; actuate the stepper motor according to a second mode when the alignment signal indicates that the current alignment of the solar collector module does not match the position of the sun, wherein at least one of a speed and a direction of pivoting of the solar collector module is different in the second mode than in the first mode.
 12. The method of claim 11, wherein the speed of pivoting of the solar collector module in the second mode is faster than in the first mode.
 13. The method of claim 11, wherein the direction of pivoting of the solar collector module in the second mode is opposite the direction of movement of the sun.
 14. The method of claim 11, wherein actuating the stepper motor according to the first mode comprises actuating the stepper motor at a rate of 1.04 seconds per step.
 15. The method of claim 11, wherein actuating the stepper motor according to the second mode comprises actuating the stepper motor at a rate of 0.01 seconds per step.
 16. The method of claim 11, further comprising detecting a predetermined end of day time and, in response thereto, actuating the stepper motor to pivot the solar collector module back to a start of day position.
 17. The method of claim 11, wherein detecting sun irradiance comprises detecting sun irradiance on at least one of a first photocell and a second photocell having a vane disposed there between.
 18. The method of claim 17, wherein actuating the stepper motor according to the first mode comprises actuating the stepper motor according to the first mode when the first photocell detects a similar amount of sun irradiance as the second photocell.
 19. The method of claim 17, wherein actuating the stepper motor according to the second mode comprises actuating the stepper motor according to the second mode when the first photocell detects a substantially different amount of sun irradiance as the second photocell.
 20. The method of claim 11, further comprising: detecting a current temperature of the solar collection module; and misaligning the solar collector module from the sun when the detected current temperature exceeds a predetermined threshold temperature. 